(1) Field of the Invention
The present invention provides methods and apparatus of improving both the gain and the bandwidth of a microstrip patch antenna.
(2) Description of the Prior Art
A patch antenna, also referred to as a rectangular microstrip antenna, is a type of radio antenna with a low profile that can be mounted on a flat surface. The patch antenna includes a flat conductor mounted on a dielectric substrate over a larger conductor, typically referred to as a ground plane. The two metal sheets of the patch antenna form a resonant piece of microstrip transmission line. The patch is designed to have a length of approximately one-half wavelength of the radio waves being transmitted or received. A patch antenna can be constructed using the same technology as that used to make a printed circuit board.
An ordinary patch antenna exhibits resonant behavior characterized by a high Q-factor and a relatively narrow impedance bandwidth on the order of 2-6 percent, depending on the losses in the antenna. Some patch antennas are formed from two stacked patches and are designed to have a double resonance, one corresponding to the L1 frequency (1575 MHz) and the other to the L2 frequency (1227 MHz) commonly used in global positioning systems. FIG. 1 provides an exemplary measured voltage standing wave ratio (VSWR) plot for such an antenna. A first resonance is indicated at L1 and a second resonance is indicated at L2.
Typical patch antennas are tuned to the L1 and L2 GPS commercial frequencies, but they lack performance at the operating frequencies of other desirable services, including new and emerging COMMs bands, such as Iridium™, which typically operates between 1616 MHz and 1626.5 MHz.
Thus, there is a need for antennas that can receive these new bands. There is a further need for adapting existing patch antennas to accommodate additional services operating at these other frequencies.